The present invention relates to a displacement control valve for a variable displacement compressor that adjusts the pressure in a control pressure chamber by supplying refrigerant from a discharge pressure region to the control pressure chamber and releases refrigerant from the control pressure chamber to a suction pressure region so as to control the compressor displacement in accordance with the pressure adjustment of the control pressure chamber.
In a variable displacement compressor that includes a control pressure chamber accommodating a swash plate with a variable inclination angle, the inclination angle of the swash plate decreases as the pressure of a control pressure chamber becomes high and increases as the pressure of the control pressure chamber becomes low. When the inclination angle of the swash plate becomes small, the stroke of a piston becomes small and the displacement of the compressor decreases. When the inclination angle of the swash plate becomes large, the stroke of a piston becomes large and the compressor displacement increases. Japanese Laid-Open Patent Publication No. 2006-342718 describes a displacement control valve for controlling the flow rate of refrigerant supplied to a control pressure chamber from a discharge pressure region through a supply passage and the flow rate of refrigerant released from the control pressure chamber into a suction pressure region through a release passage to adjust the pressure of the control pressure chamber.
If the variable displacement compressor is not operated for a long period of time, refrigerant liquefies and collects in the control pressure chamber. When the variable displacement compressor is activated in a state in which liquefied refrigerant is collected in the control pressure chamber, if the displacement control valve keep the cross-sectional area of the regulation passage in a small state, the liquefied refrigerant cannot be readily released from the control pressure chamber to the suction pressure region through the regulation passage. This may increase the pressure of the control pressure chamber to an excessively high level due to vaporization of the liquefied refrigerant in the control pressure chamber. Thus, too much time would be required for the variable displacement compressor to increase displacement after activation.
The displacement control valve described in the above publication includes a bellows, an electromagnetic solenoid, and a valve body driven by the electromagnetic solenoid. The valve body is connected to a drive rod of the electromagnetic solenoid. A connection portion is connected to the valve body, and an engagement portion, which is contactable with the connection portion, is connected to the bellows. A relief passage extending to a suction chamber (suction pressure region) is formed in the valve body. The pressure (suction pressure) in the relief passage acts on the engagement part joined to the bellows. A displacement chamber formed outside the bellows is in communication with the control pressure chamber and is communicable with a discharge chamber (discharge pressure region) through a valve hole in the valve body. A valve portion opens and closes the valve hole.
When the variable displacement compressor is activated in a state in which liquefied refrigerant is collected in the control pressure chamber, the liquefied refrigerant flows into the displacement chamber. This contracts the bellows and moves the engagement portion, which is connected to the bellows, away from the connection portion. This enables the liquefied refrigerant in the control pressure chamber to be released into the suction pressure region and thereby shortens the time required for the compressor displacement to increase after activation of the variable displacement compressor.
The relief passage, which is for releasing refrigerant from the control pressure chamber into the suction pressure region, includes a terminal portion, which extends perpendicular to a linear shaft passage extending through the drive rod along the axis of the drive rod and opens in an outer surface of the drive rod. The terminal portion of the relief passage is a linear passage. Accordingly, the structure in which the linear shaft passage and the linear terminal portion extend perpendicular to each other in the drive rod increases the flow resistance. This is not preferable for readily releasing the liquefied refrigerant.